This invention relates to improvements in an oil separator disposed inside a cylinder head cover of an internal combustion engine to separate oil mist from blowby gas discharged outside through the cylinder head cover.
For example, in an automotive internal combustion engine, blowby gas containing unburned components and leaked from a combustion chamber to a crankcase is introduced through an engine intake system into the combustion chamber to burn the unburned components together with fresh air taken in from outside, as well known. Blowby gas passing through the inside of the crankcase contains oil mist, and therefore an oil separator is disposed at a part of the cylinder head cover as disclosed in Japanese Patent Provisional Publication Nos. 2005-120855 and 2009-121281 in order to prevent oil mist from being carried to the engine intake system. After oil mist is separated and removed by this oil separator, blowby gas is taken out from the inside of the cylinder head cover. In general, two blowby gas passages are connected to the cylinder head cover, in which fresh air is introduced through one of them under a normal operating condition, while blowby gas flows through both of them under a high engine load operating condition. Accordingly, two oil separators are respectively provided in the two blowby gas passages.
The oil separator disclosed in the Patent Provisional Publications is a so-called inertial collision-type oil separator, in which a partition wall formed with many passage holes is disposed inside an oil separator chamber, and a collision plate is disposed adjacent to this partition wall in such a manner as to be opposite to the passage holes. The flow velocity of blowby gas containing oil mist becomes high when blowby gas passes through the passage holes of the partition wall, so that blowby gas strikes against the collision plate at a high speed after getting out of the flow passages so that oil mist adheres onto the collision plate and recovered. The collision plate is formed at its bottom section with a slit-like opening through which oil grown as large droplets upon being separated by the collision plate is flown along the bottom surface of the oil separator to a downstream side and then dropped into a valve operating chamber through the bottom end discharge outlet of a drain pipe disposed at the bottom wall of the oil separator.
Here, in general, the passage holes formed in the above partition wall is circular in cross-section as disclosed in Japanese Patent Provisional Publication No. 2005-120855. In this regard, Japanese Patent Provisional Publication No. 9-96209 discloses an oil separator using passage holes which are rectangular or hexagonal in cross-section though the oil separator is different in basic configuration from that of the above two Japanese Patent Provisional Publications.